Foam pads useful in wound management

ABSTRACT

The present invention relates to a method of dressing a wound using an open-celled foam pad prepared from a foam sheet impregnated with a water curable, isocyanate functional, polyurethane prepolymer resin. The pad can concurrently function as an orthotic pad. The pad exhibits the ability to wick wound exudate from the site of the wound, and also exhibits desirable conformability and comfort in use.

This is a division of application Ser. No. 07/800,571 filed Nov. 27,1991 now U.S. Pat. No. 5,203,764 issued Apr. 20, 1993 which is acontinuation-in-part of Ser. No. 07/674,565, filed Mar. 25, 1991, nowU.S. Pat. No. 5,195,945.

TECHNICAL FIELD

The present invention relates to the field of wound management anddressings, and in particular, to the use of foam dressings in woundmanagement.

BACKGROUND ART

The field of orthotic pads, and materials useful therefore, is describedin co-pending application Ser. No. 07/674,565.

The field of foam dressings in wound management is described, forinstance, in S. Thomas, Wound Management and Dressings, ThePharmaceutical Press (1990) (see, for example, Chapter 5, "FoamDressings", and references cited therein).

SUMMARY OF THE INVENTION

The present invention provides a foam pad useful for dressing a wound.The use of the foam pad as a wound dressing can be, and preferably is,in addition to its concurrent use as an orthotic pad, for instance, whenthe orthotic pad is in the form of a cast padding as described inco-pending U.S. application Ser. No. 07/674,565. In another aspect thepresent invention provides a wound management kit comprising a foamblank that can be cured by the user in order to prepare a foam pad,together with interface material(s), and overwrap means.

Surprisingly, it has been found that a foam pad of the present inventionperforms exceptionally well as a cast padding, not only for the reasonsdescribed in the above co-pending application, but also in situations inwhich there already exist open, exudate-producing incisions or wounds inthe area covered by the cast. Additionally, comfort of the patient isimproved, without the added weight and decreased permeability often seenover the course of using a conventional fiberglass cast lined withplaster. The foam pad appears to be able to substantially retain itsporosity and to wick exudate away from the wound, thereby resulting in amuch improved environment for healing the wound or incision.

The foam pad also appears to be able to better grip the skin of thepatient, in comparison to a cotton padding, thereby improving theimmobilization effect of cast. This results in reduced motion betweenthe cast and limb, and thereby also appears to result in a reduction ofpressure sores and sores due to cast movement. The use of the foam padencourages the use of casts in situations, e.g., in veterinary use,where a marginal indication may be otherwise outweighed by the fear ofpressure sore formation. In situations, for instance, of the prospectivesale or show of an injured horse, the fear of complications from castingoften discourages its use. In these instances, a cast with a foam pad ofthe present invention could be safely used with less fear of unduecomplications. This would be particularly true in the treatment of foalswith injuries or deformities that would benefit from cast application.

As described more fully below, a foam pad that is used with a suitablecasting material, e.g., a fiberglass casting tape, can cure to become anintimate part of the cast and therefore will neither be displaced ormove within the cast after application. The foam pad is stable enough inits adherence to the cast tape that it also makes cast removal easierand safer, particularly for a cast that is closely applied to the limb.Since the foam pad is typically less rigid than a fiberglass castmaterial, the foam pad does not cut as readily with the cast saw as doesthe fiberglass cast material. This adds an additional layer ofprotection between the cast saw and the patient's skin. Cast removal cantherefore be an easier and safer task than what is encountered aftertraditional cast application.

According to a presently preferred embodiment of the invention, a foamblank is provided which comprises a conformable, curable substrate.Preferably, the foam blank comprises an open-celled foam sheetimpregnated with a water-curable, isocyanate functional, prepolymerresin. The foam pad is formed from the blank by activating theprepolymer resin, applying and conforming the blank to a part of thebody, and holding the blank in place as it sets. When cured, theresultant foam pad bears an impression of the body part, i.e., it isclosely and permanently conformed to the shape and position of the bodypart held in apposition to the blank during curing. The cured foam padalso exhibits both proper weight-bearing strength and cushioningproperties, in order to support and/or cushion that body part, ifdesired.

The modulus of the cured foam pad, as defined below, can be determinedand used as an indication of the ability of the pad to comfortablysupport weight, while the resilience, also defined below, can bedetermined as well, and used as an indication of the cushioningproperties of the cured pad. Significantly, the resultant cured pad canexhibit "variable modulus and resilience", i.e., the modulus andresilience of portions of the resultant pad will vary according to thedegree each portion was compressed as it cured. As a result, the abilityof the cured pad to support and/or cushion the body part directlycorrelates with the needs of each portion of the opposing body part. Thepad is most dense, and therefore has a higher modulus and is slightlymore resilient, in areas where it was most compressed during curing. Asa result, denser areas are better able to provide support, whereas lessdense (lower modulus, slightly less resilient) areas are better able toprovide a cushion effect.

Because the foam sheet itself, before impregnation with resin, is pliantand extensible, the conformability of the resin impregnated foam pad isquite good. Surprisingly, the foam sheet can be resin loaded to a veryhigh degree and thereby impart the modulus and resilience desired in thecured foam pad. Also surprisingly, after resin loading the foam sheet tothe extent necessary to achieve the desired properties, the resultantfoam pad still exhibits variable modulus and resilience.

The foam sheets of the present invention can frequently be impregnatedin a solvent-less manner, thereby avoiding any potential problem arisingfrom prolonged contact of residual traces of solvent with the body part.

Good conformability, moldability and omnidirectional extensibility inapplying the resin impregnated foam sheet are made possible with thepresent invention. As a result, good alignment of the cured foam padwith respect to the body part can be achieved. Another benefit of thepresent invention is that the surface of the resin impregnated foam padis less tacky than would be expected, thereby greatly facilitatingapplication of the pad. Furthermore, by the addition of catalysts asdescribed herein, the blanks of the present inventions are able to beset and cured within a short period of time, yet with a low exotherm,thereby providing both convenience and comfort for the subject.

Foam pads of the present invention can be provided alone or in a kit,e.g., a kit that includes suitable interface material(s) and suitableoverwrap means, such as casting tape or elastic bandage, as well asinstructions for use and/or other suitable components such asmedicaments.

These and other features of the present invention will become more fullyapparent from the following description and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a resin impregnated foam pad of theinvention wrapped around a patient's lower leg;

FIG. 2 is a cross sectional view taken along section line 2--2 of FIG.1.

DETAILED DESCRIPTION

The subject matter of the present application is a continuation-in-partof the subject matter of the copending application cited above.

The subject matter of the co-pending application is directed to the useof the described foam pads as orthotic pads, and methods for formingsuch orthotic pads. The present invention provides that the materialsdescribed in the co-pending application are additionally andindependently useful in wound management, i.e., as wound dressings. Insome instances, the same foam pad will perform both functions, i.e., itwill be used as an orthotic pad as previously described, and willconcurrently serve as a wound dressing for wounds that exist in the areacontacted by the pad. In other instances the foam pad will be usedsolely as a wound dressing, i.e., retained in contact with a wound,however not used to simultaneously cushion or support.

The present invention, in one aspect, provides a method of dressing awound comprising the step of placing in fluid contact with the wound afoam pad prepared from a foam blank comprising an open-celled foamimpregnated with a resin system, the resin system comprising

a. a water curable prepolymer resin comprising an isocyanate componentand a polyol component, said polyol component having an average hydroxylequivalent weight greater than about 400 grams of polyol per hydroxylgroup, and

b. a catalyst capable of setting and curing said prepolymer resin uponexposure to water.

The word "wick" as used herein refers to the ability of the foam totransport liquids such as wound exudate from the area of the wounditself through the foam, e.g., to the surface of a compressing materialsuch as a cast or bandage overwrap. The overwrap would typically beadjacent to the surface of the pad that is opposite to the surfacecontacting the wound. The word "contact" as used in the presentapplication will be used interchangeably with the term "fluid contact",to mean that the pad is capable of wicking fluids from the wound siteregardless of the presence of an interface material, such as astockinette or gauze, between the pad and the wound. Generally, andpreferably, pads of the present invention will be used with such aninterface material. Any suitable interface material can be used thatdoes not interfere with fluid contact between the wound site and the padto the point where the foam pad would not serve its intended purpose.

The word "modulus" as used herein refers to the force required toproduce a unit of deformation, e.g., compression, in a cured resinimpregnated foam, i.e., modulus equals force/deformation. As such, itreflects the ability of the cured foam to comfortably support a bodypart, e.g., to provide proper weight-bearing strength for use inorthopedic applications. In turn, the "inverse of modulus" equalsdeformation/force. Thus, by using a constant force to compress differentfoams, one can measure and compare the percent deformation that eachcured foam undergoes under that constant force.

The word "resilience", and inflected forms thereof, as used hereinrefers to the ability of a cured, resin impregnated foam that has beencompressed, to recover substantially its original dimensions within agiven period of time. As such, it reflects the ability of the cured foamto provide a cushioning effect, i.e., to recover its cured shape withina period of time after compression, e.g., during use, such as walking inthe case of an orthotic footpad. As will become apparent to thoseskilled in the art, modulus and resilience are dependent in part on suchfactors as the nature and/or density of the foam, the nature and/oramount of resin impregnated in the foam, the weight and/or cured densityof the final unitary blank, and the extent of compression of the foamduring curing, i.e., its initial density compared to its cured density.

A blank of the present invention is generally comprised of a pliant,extensible foam sheet. The foam sheet is open-celled, and a curableresin is impregnated in the foam sheet. As used herein, the term"open-celled" refers to a foraminous structure having interconnecting orcommunicating orifices or cavities therein caused by a sufficient numberof the wall membranes of the foam cells having been removed. Further, asused herein, the word "impregnated" and inflected forms thereof refersto the condition in which the resin is intermingled with and insurrounding relation to the wall membranes of the cells and theinterconnected cells of the blank.

The foam sheet can comprise any one of a number of extensible foams thatare open-celled, such as polyether- or polyester-based polyurethanefoams. Importantly, the porosity of the blank must be such that it canbe resin loaded sufficiently to provide a satisfactory pad. In thisregard, the open-celled foam sheet preferably has from about 10 to about50 pores per centimeter (i.e., about 30 to about 120 pores per inch). Asused herein, the term "pores per centimeter" refers to the averagenumber of pores located along a linear centimeter of the foam sheet. Thenumber of pores per linear centimeter may be determined in a number ofways known to those skilled in the art, for example, byphotomicrographic means, or by measuring the foam's resistance to airflow or a pressure differential, and using such information to calculatethe approximate number of pores in the foam.

When the number of pores per centimeter is decreased below about 10, thefoams become too coarse or rough, and typically do not hold enough resinto either provide the necessary strength for the resulting pad or toretain the desired conformation. Foam sheets having over about 50 poresper centimeter are not known to be presently commercially available. Itwill be understood, however, that the maximum number of pores percentimeter parameter is limited solely by the ability to load the foamwith enough resin to provide sufficient properties for use as a wounddressing pad. Since foam sheets having over 50 pores per centimeter arenot presently available commercially, it is difficult to predict theperformance of foams having substantially more than 50 pores percentimeter, e.g., as to their resin loading characteristics andporosity. Preferably, the open-celled foam sheet used to form blank 10has from about 20 to about 40 pores per centimeter.

The dimensions of the foam sheet depends in large part on the intendeduse of the pad. A blank of the present invention can be prepared andpackaged having dimensions intended for use in apposition to aparticular type and/or size of body part. Generally, the most importantdimension will be the thickness of the blank, i.e., the distance(s)between the major surface to be contacted with the body part, and theopposite surface thereto. The other dimensions of the foam sheet, e.g.,those that determine the surface area of the body part to be supportedand/or cushioned can be varied as desired, as will become apparent tothose skilled in the art. Uncured blanks or cured pads can generally betrimmed, as with a blade or scissors, or by grinding or abrading,respectively, to provide a desired size and shape.

Suitable blanks will typically be of a thickness between about 0.5 cmand about 5 cm, and preferably between about 1 cm and about 3 cm. Thefoam sheet need not be of uniform thickness either, particularly insituations, for example, where a portion of a body part requiresadditional support or cushioning. For use as a pad within animmobilizing device, such as a cast, the foam pad will typically beprovided in the shape of a tape. The pad is sufficiently dimensioned toencompass the area of the body part to be covered.

Similarly, the resin impregnated foam sheet can be used alone or incombination with other materials, e.g., to vary its thickness, toprovide additional strength, to provide a custom wear surface, to morewidely vary its density and so forth. Such other materials can include,for instance, resin impregnated knit fabrics, or other resin impregnatedfoam sheet materials, e.g., utilizing a different foam and/or resin inorder to provide such different properties. These other materials couldalso include such materials as plastics, leather, metal and the like andmay be applied before, during or after setting or curing of theimpregnated foam. Preferably, such other materials are of a type thatwill bond themselves to the orthotic blank as it cures, by virtue of theinherent adhesive qualities of the resin used in the blank.

The foam sheet utilized in the foam blank preferably has a density inthe range of about 0.02 to about 0.15 g/cm³, and most preferably,between about 0.02 and about 0.07 g/cm³. Foam sheets possessingdensities lower than about 0.02 g/cm³ are not known to be presentlycommercially available. Foam sheets having densities higher than about0.15 g/cm³ tend to preclude the ability to resin load the foam to theextent necessary to achieve proper strength.

Examples of suitable foam sheets include "E-100", "E-290", "P-60","P-80" and "P-100", each available from Illbruck U.S.A., Minneapolis,Minn. One presently preferred material for the foam sheet of the presentinvention is a polyether-based polyurethane foam sheet that isapproximately 2 cm thick and is presently available from Illbruck USA,as type "E-150".

The most preferred resins for impregnating the foam sheet materials ofthe present invention are water-curable, isocyanate functional,polyurethane prepolymers prepared by the reaction of a polyol with anexcess of a polyisocyanate. Suitable resins are disclosed, e.g., in U.S.Pat. Nos. 4,419,261 and 4,968,542, the disclosures of which are herebyincorporated by reference.

In order to obtain the desired modulus and resilience in a cured pad ofthe present invention, a significant factor in the choice of anappropriate polyol and an appropriate polyisocyanate to form thepolyurethane prepolymer resin is the average hydroxyl equivalent weight,that is, the average molecular weight of the polyol(s) divided by theaverage number of reactive hydroxyl (OH) groups per mole of polyol(s).In general, the average hydroxyl equivalent weight of the polyol orpolyol blend will be between about 400 grams and about 2400 grams, morepreferably between about 1000 grams and about 2000 grams, and willpreferably be greater than about 1000 grams when the isocyanate ispolyaromatic, such as diphenylmethane diisocyanate.

Suitable polyols for use in the prepolymer resin include polyalkyleneethers derived from the condensation of alkylene oxides (such as thoseavailable from Union Carbide, South Charleston, W.Va., under thetradename "Niax" and from BASF Wyandotte Corp. under the tradename"Pluracol"), polytetramethylene ether glycols (such as the "Polymeg"polyols available from the Quaker Oats Co.), polycaprolactone polyols(such as the "Niax PCP" series of polyols available from Union Carbide),and polyester polyols (hydroxyl-terminated polyesters obtained fromesterification of dicarboxylic acids and diols) such as the "Rucoflex"polyols available from Ruco division, Hooker Chemicals Co.

Examples of specific polyols that are useful include polypropyleneglycols such as "PPG 2025" and "PPG 3025" available from Union Carbide,polypropylene triols such as "LHT 42" and "LHT 34", available from UnionCarbide, and tetrols such as "Tetronic 1501" available from BASFWyandotte Corp., Parsippany, N.J. Preferably all polyols used areurethane grade. The term "urethane grade" as used herein refers topolyols having a purity grade suitable for polyurethane production, asdescribed, e.g., in Appendix B of Polyurethanes--Chemistry andTechnology, J. H. Saunders and K. C. Frisch, eds., R. E. KriegerPublishing Co., Huntington, N.Y. (1978), the disclosure of which ishereby incorporated by reference.

However, it will be understood that, as used herein, the term "polyol"also includes virtually any functional compound having active hydrogenin accordance with the well-known Zerevitinov test, as described, forexample, in Chemistry of Organic Compounds by Carl R. Noller, Chapter 6,pp. 121-122 (1957) the disclosure of which is hereby incorporated byreference. Thus, for example, thiols and polyamines could also be usedas "polyols" in the present invention and the term "polyols" will beconsidered to include such active hydrogen compounds. In such instances,the NCO:active hydrogen ratio of the polyisocyanate to the activehydrogen compound used to form the polythiocarbamate, polyurea, or otherpolymer, should fall within the same ranges as disclosed herein for theNCO:OH ratios.

Also in the present invention, the isocyanate equivalent weight of theprepolymer used is preferably relatively large. The isocyanateequivalent weight of the prepolymer is defined as the grams ofprepolymer (i.e., polyol and isocyanate) per NCO group in theprepolymer. For purposes of the present invention, it has been foundthat the isocyanate equivalent weight should be within the range ofabout 400 grams to about 2300 grams of prepolymer per NCO group, andmost preferably within the range of about 700 grams to about 1500 gramsof prepolymer per NCO group.

Examples of isocyanates used to form polyisocyanates that are suitablefor purposes of the present invention are disclosed, e.g., in U.S. Pat.Nos. 4,376,438, 4,433,680, and 4,502,479. Those isocyanates that arepresently preferred include 2,4'-diphenylmethane diisocyanate,4,4'-diphenylmethane diisocyanate, mixtures of these isomers togetherwith possible small quantities of 2,2'-diphenylmethane diisocyanate(typical of commercially available diphenylmethane diisocyanates), andaromatic polyisocyanates and their mixtures, such as are derived fromphosgenation of the condensation product of aniline and formaldehyde. Itis presently preferred to use an isocyanate that has low volatility,such as diphenylmethane diisocyanate, rather than a more volatilematerial such as toluene diisocyanate. Commercially available isocyanatestarting materials include "Isonatex® 143L" available from Dow Chemical,LaPorte, Tex., which is a mixture of isocyanate compounds containingabout 73% by weight of diphenylmethane diisocyanate; "Mondurx® MRS-10"available from Mobay Chemical Corp., New Martinsville, W.Va.; and thepolyaromatic polyisocyanate, "PAPI" available from Dow Chemical.

The NCO:OH ratio of the components of the prepolymer resin is preferablywithin the range of about 2:1 to about 8:1, and most preferably withinthe range of about 2.5:1 to about 4:1. It has been found that NCO:OHratios lower than about 2:1 do not provide enough excess isocyanategroups to achieve adequate cross-linking of the resin during cure, whileNCO:OH ratios greater than about 8:1 tend to produce undesirablestiffness. Higher NCO:OH ratios, i.e., approaching about 8:1, wouldgenerally be useful with polyols having higher hydroxyl equivalentweights.

Especially preferred resin components for use in the pads of the presentinvention are "Mondurx® MRS-10" isocyanate and "LHT-34" polyol availablefrom Union Carbide. Another preferred resin may be formed by reactingthe "Isonatex® 143L" isocyanate and the polypropylene oxide polyolavailable from Union Carbide as "LHT-42". To prolong the shelf life ofblanks, it is preferred to include about 0.02 to about 0.1 percent (byweight based on the weight of the prepolymer resin) of benzoyl chlorideand/or other suitable stabilizer (e.g., an antioxidant such as butylatedhydroxy toluene at a level of about 0.05 to about 0.25 weight percent).

The term "resin system" as used herein refers to the prepolymer resinitself, i.e., the combination of polyol and isocyanate, as well as anyother ingredients (e.g., catalyst(s), stabilizer(s), plasticizer(s),antioxidant(s), and the like) added to the prepolymer resin, or toeither the polyol or isocyanate components thereof, prior to orsimultaneously with their impregnation into the foam.

The resin systems of the present invention preferably contain a catalystto control the set time and cure time of the resin. The term "set time"as used herein refers to the time needed for an activated blank to holdits conformed shape. At this time it could be removed from contact withthe body part while it continues to cure. The term "cure time" as usedherein refers to the time needed for the resin therein to cross-link tothe furthest extent it is going to cross-link under the conditionschosen.

During the set time the activated blank should exhibit an exothermcompatible for use in apposition to a mammalian body part, e.g.,preferably an exotherm of less than about 43° C. and more preferablyabout 40° C. The resin system of the present invention, as will becomeapparent to those skilled in the art, can be adjusted in a variety ofways to obtain suitable exotherm during cure, e.g., by decreasing theresin loading level; increasing the isocyanate equivalent weight of theprepolymer resin; reducing the NCO:OH ratio, and the like.

To produce suitable pads in accordance with the present invention, a settime of less than about 20 minutes following activation of the resin byexposure to water is preferred, with the most preferable set time beingless than about 10 minutes. Frequently set times on the order of about 5minutes or even about 4 minutes or about 3 minutes can be achieved.Suitable catalysts for moisture curing such prepolymer resins willbecome apparent to those skilled in the art. For example, tertiaryamines such as 2,2'-dimorpholinodiethyl ether (DMDEE) described in U.S.Pat. No. 4,433,580, and 2,2'-dimorpholinyldialkyl ethers such as4-[2-[1-methyl-2l-(4-morpholinyl)ethoxy]ethyl]morpholine (MEMPE)described in commonly assigned U.S. Pat. No. 4,705,840, in amountsranging from about 0.5% to about 7% and preferably from about 2% toabout 5% by weight, based on the weight of the prepolymer resin, may beused for this purpose.

Plasticizers can be, and preferably are, incorporated into the orthoticblank in order to maintain resilience of the cured orthotic pad overtime, in a manner that will become apparent to those skilled in the art.For example, a plasticizer such as butyl benzylphthalate, available fromMonsanto ("Santicizer 160") can be added to the resin system at betweenabout 1% and about 20% by weight, based on the weight of the prepolymerresin. A preferred amount of this plasticizer is between about 8% andabout 12% by weight. The use of a plasticizer is particularly preferredin order to prepare resins having NCO:OH ratios approaching about 8:1,in that resins having such higher ratios (e.g., greater than about 4:1)tend to be stiff when used without plasticizer.

Preferably, and particularly when the pad is to be used in apposition tothe skin itself, the resin system used therein is impregnated into thefoam sheet in a solvent-less manner, i.e., without the use of solventssuch as organic solvents, e.g., methylene chloride, and the like.Generally, resins having a viscosity of about 100,000 centipoise or lesscan be impregnated into the foam sheets without the use of solvents bymethods that will become apparent to those skilled in the art, e.g., bymanually squeezing or otherwise manipulating the resin system into thefoam.

Resin systems having higher viscosities, e.g., greater than about100,000 cps can generally also be impregnated into foam sheets withoutthe use of solvents, e.g., in the manner described in commonly assignedU.S. Pat. No. 4,946,726, wherein the polyol and isocyanate components ofthe prepolymer resin are blended immediately before impregnating into afoam sheet and allowed to react in situ in the foam sheet to form theprepolymer resin.

Preferably, the foam sheets of the present invention are impregnatedwith resin systems at coating weights of at least about 30% by weight ofthe total material, preferably at least about 40% by weight andparticularly preferred are coating weights of at least about 50% byweight. Surprisingly, the prepolymer resin can often be impregnated intothe foam sheets of the present invention so as to comprise as much as80%, 90%, and even 95% by weight while still retaining suitable moduli,resilience and conformability, depending on the foam and on the resinchosen.

The resin impregnated foam sheets of the present invention arepreferably prepared in a relatively low humidity chamber and sealedwithin a water vapor-impermeable package. This package is opened justprior to application of the blank.

Elements of the pads of the present invention and a presently preferredmethod by which pads can be formed and used as wound dressings will nowbe described.

A blank is preferably used by: 1) "activating" the prepolymer resin,i.e., exposing the blank to water to initiate setting and curing of theresin; 2) if necessary, manually squeezing out excess water; 3) properlypositioning the pad on the patient, if necessary with the use of one ormore appropriate interface materials; 4) keeping the pad in place as theresin sets, with sufficient pressure to cause the surface of the pad tobecome conformed to the shape of the patient's body part, and, ifnecessary; 5) trimming excess material from the cured pad in order toachieve the desired pad size or shape. The cured pad bears an impressionof the body part, i.e., it conforms closely and permanently to the shapeand position of the body parts held in apposition to the blank duringcuring. The cured pad also provides proper weight-bearing strength andcushioning properties for its intended use, and, depending upon thevarying degrees to which each portion of the blank was compressed duringcuring, the resultant pad exhibits variable modulus and resilience.

Before actually applying a blank to a body part, a flexible stockinet orother suitable interface material is preferably placed between thesubject's skin and the blank so as to prevent undesirable adhesion orcontact between the blank and the body part. One or more interfacematerials can be used, e.g., a stockinette can be used to generallycover the overall area covered by the pad, together with a secondinterface material, such as a wound contact interface material that isspecifically used to cover the area of an open wound.

Preferably the wound contact material is sufficiently porous to woundexudate to allow fluid contact to be established between the wound andthe outerlying pad. More preferably, the wound contact interfacematerial is of the type identified in Chapter 3, "Primary Wound ContactMaterials" of the above-cited Wound Management and Dressings, S. Thomas,the entire disclosure of which is incorporated herein by reference. Inparticular, the materials identified by the heading as "AlternativeForms of Dressings with Low Adherence" (pp. 22-23) are desirable for useas interface materials in the present invention.

Such "non-adherent" wound contact interface materials are typicallytransparent and hypoallergenic, and provide two-way transport of gasesand moisture, thereby allowing the wound to maintain a moistenvironment. Such materials are typically made from polymeric sheets,webs, or films. Examples of suitable non-adherent wound contactmaterials include Tegapore™ material (3M), Transite™ material (Smith &Nephew), and Telfa™ material (Kendall).

To expand further on the above description, a pad is formed by firstactivating the resin of the blank with water. This can be accomplished,for example, by exposing it to water, e.g, dipping it in water, sprayingit with water, and so on. Next, the blank is preferably placed on oragainst the body part or another surface, e.g., a solid, flat surface,and aligned with the body part. In this regard, the resin impregnatedfoam has excellent compression moldability and conformability to providea good fit to the shape of the body part.

The pad is retained compressed to the desired extent against the bodypart while the resin sets, optionally by the aid of overwrap meansretaining the pad in place. The selection of suitable overwrap means candepend on the intended use of the foam pad. For instance, when the padis to be used as a cast padding, the overwrap means can be the castingtape itself. When the pad is to be used in some other manner, e.g.,solely as a wound dressing and not also as an orthotic pad, othersuitable means can be used as an overwrap.

The term "overwrap means" as used herein refers to the means used toinitially retain the pad in position as it cures, and/or the means usedto retain the cured pad in position over the course of its subsequentuse. These means can be the same or different. In the latter case, forinstance, it might be desirable to use means that merely retain the padin position with no compressive pressure, or with either less or morecompressive pressure than might have initially been used to cure thepad. When the pad is applied to a limb, for instance, such means couldinclude anything from a circumferential, overlapped, wrapping of the padand limb with an elastic bandage, to the use of a piece of standardsurgical tape that extends sufficiently beyond the edges of the pad toretain the pad in position on the skin.

It will be understood that various modifications and changes may be madeby those skilled in the art to accommodate different situations.

The present invention will be further understood in view of thefollowing Examples which are merely illustrative and are not to beconsidered as comprehensive or limiting in any way. Examples 1-14 willbe repeated from co-pending U.S. application Ser. No. 07/674,565 inorder to provide relevant information regarding the taking andevaluation of materials useful in the present invention.

EXAMPLE 1

In this Example, an orthotic footpad within the scope of the presentinvention was prepared. First, a polyether-based polyurethane foam,having a thickness of approximately 1.95 cm was obtained from IllbruckU.S.A. (Minneapolis, Minn.) as type "E-100". This foam material has adensity of about 0.02 g/cm² and a pore size of about 24 pores per linearcentimeter. A 10.2 cm by 30.5 cm sheet of this foam material was cut outwith a scissors. The weight of the foam sheet was determined to be about12 grams, and this figure was used to determine the correct amount, ingrams, of the resin system to be used in order to achieve a resinloading of about 85% by weight of the final resin impregnated foamsheet.

A polyurethane prepolymer resin having an NCO:OH ratio of about 3.0:1was prepared as follows. In an atmosphere maintained at about 4%relative humidity, a vessel was charged with 396 grams of isocyanate("Mondurx® MRS-10," obtained from Mobay Chemical). (This isocyanatecompound has an NCO equivalent weight of about 132 grams of isocyanateper NCO group.) A second vessel was charged with 1650 grams of "LHT-34"as the polyol, which was obtained from Union Carbide. (The LHT-34 had anOH equivalent weight of about 1650 grams of polyol per OH group.) To theLHT-34 in the second vessel was added 0.4 grams of benzoyl chloride asstabilizer, 236 grams of butyl benzylphthalate ("BBPTH", Monsanto) asplasticizer, and 85 grams of4-[2-[1-methyl-2-(4-morpholinyl)ethoxy]ethyl]morpholine ("MEMPE" ) ascatalyst, prepared as described in Example 1 of commonly assigned U.S.Pat. No. 4,705,840, the disclosure of which is hereby incorporated byreference. The mixture in the second vessel was then added to theisocyanate compound contained in the first vessel, and the componentswere blended together. (This prepolymer mixture had an NCO equivalentweight of about 1023 grams of prepolymer resin per NCO group.)Immediately after blending these components together, the blended resinsystem was impregnated into the foam sheet in an amount such that theresin system represented about 85% by weight of the final product. Suchimpregnation of the resin system into the foam sheet was achieved in amoisture-free chamber by spreading the resin system over all surfaces ofthe foam sheet and then manually kneading the resin system into the foammaterial. The viscosity of the resin system 24 hours after blending thecomponents (to allow sufficient time for reaction to occur) wasdetermined to be about 20,000 centipoise, using a Brookfield viscometer,Model RV, Brookfield Engineering Laboratories, Stoughton, Mass. Theblank thus prepared was then sealed in an air-tight pouch to protect theblank from exposure to moisture.

Later, the blank prepared in this Example 1 was applied to a foot by thefollowing procedure. The impregnated foam blank was removed from thepouch, and activated by dipping in room temperature water. Excess waterwas removed by squeezing. The activated, impregnated foam blank wascovered with a 0.038 mm (1.5 mil) thick film of Elastoflex "P",available from Clopay Co. A subject's bare foot was then settled intothe foam blank causing the foam to conform in shape to the heel, soleand lower sides of the foot. Care was taken not to completely compressthe foam under the heel or ball of the subject's foot.

After being held in place for about five minutes, the foot was removedfrom the foam blank leaving an exact impression of the subject's foot.The Elastoflex "P" film was peeled off and when cured, the orthotic padwas trimmed as necessary with a scissors and hand held grinder (Dremel"Moto Tool", Sears Roebuck) to fit the subject's shoe as an insert. Thefinished insert conformed exactly to the subject's foot, providedexcellent support and cushioning, particularly in the arch area, and wascomfortable to wear.

EXAMPLE 2

In this example, an orthotic shinpad within the scope of the presentinvention was prepared according to the procedure of Example 1 with thefollowing exceptions. In this Example 2, a polyurethane prepolymer resinhaving an NCO:OH ratio of about 2.5:1 was prepared by charging the firstvessel with 360 grams of isocyanate ("Isonatex® 143L", obtained fromUpjohn and having an NCO equivalent weight of about 144 grams ofisocyanate per NCO group). The second vessel was charged with 1335 gramsof polyol ("LHT-42", obtained from Union Carbide), and 0.17 grams ofbenzoyl chloride as stabilizer, 188 grams of BBPTH as plasticizer, and67 grams of MEMPE as catalyst. In this example, the resin system, i.e.,the prepolymer resin itself as well as the stabilizer, plasticizer andcatalyst represented about 80% by weight of the final product, and theprepolymer resin had an NCO equivalent weight of about 1130 grams ofprepolymer resin per NCO group. The blended resin system had a measuredviscosity of approximately 22,000 centipoise. A stockinette was placedover a subject's lower leg. The water activated, impregnated foam blankwas positioned against the stockinette and over the shin area. Using astretch bandage overwrap, the impregnated foam blank was partiallycompressed and conformed to the shin as it cured. The temperature thatwould be felt by the patient during curing was determined to be lessthan about 39° C., using a thermometer placed under the blank as itcured. The orthotic shinpad formed in this example was sufficiently setafter about 5 minutes from the initial activation of the prepolymerresin. The cured shinpad was trimmed to remove any excess material. Thefinished pad was soft and resilient and retained the exact shape of thesubject's shin. When held in place with an elastic bandage orstockinette the pad offered excellent protection for the shin.

EXAMPLES 3-14

The inverse modulus and resilience of a variety of pads of the presentinvention were compared by the following means, using force and timevalues that roughly approximate the forces and times an orthotic footpadwould be expected to be subjected to in the course of a subject walking.

The inverse modulus values given below represent the observed percent(%) deformation of each cured pad in response to a load of 1.05 kg/cm³(15 psi) applied over a period of 0.5 seconds.

Resilience was calculated as the percent of its original dimensions acured pad recovers within 0.5 seconds, after being deformed (compressed)to one-half of its cured thickness.

Both inverse modulus and resilience were calculated for orthotic padscured at both 0 and 50% compression, i.e., cured at both their original,uncompressed, thickness, and cured at a 50% compressed thickness.

The experimental method used to calculate modulus and resilience was asfollows:

Cyclic stress-strain experiments were performed using an MTS 810Material Test System (MTS Systems Corp., Minneapolis, Minn.). Allexperiments were performed at a frequency of 1 Hertz in a haversinedisplacement mode as controlled by the 410 Digital Function Generator.The 442 Controller was adjusted so that actuator displacement and loadcell output corresponded to 1.27 cm/volt (0.5 inch/volt) and 13.6kg/volt (30 pounds-force/volt), respectively. All loads were measuredusing an MTS Model 661.21A-01 Load Cell. Actuator linear variabledisplacement transducer "LVDT" and load cell voltages were recorded by aNicolet 4094 Digital Oscilloscope. (Nicolet Instruments, Madison, Wis.)

A 10.16 cm (4 inch) diameter, 2.54 cm (1 inch) thick steel disc testfixture was attached to the MTS load cell. A 15.24 cm (6 inch) diameter,2.54 cm (1 inch) thick steel disc test fixture was attached to the MTSactuator. As employed for testing, the load cell and actuator discs werecoaxially aligned and the faces of each disc were parallel to eachother. The test specimen was sandwiched between these two discs astested. Movement of the actuator disc toward the load cell disc wouldresult in sample compression and produce a force on the load cell disc.

Tested samples measured approximately 12.7 cm×15.24 cm (5 inch×6 inch).In all cases samples were sufficiently wide enough to completely coverthe face of the load cell disc. The tested samples were 1.65 to 2.16 cm(0.65 to 0.85 inch) thick for the uncompressed-cured samples and 0.83 to1.08 cm for the 50% compressed-cured samples.

To obtain the inverse modulus (% deformation) values, the MTS system wasused in the load control mode where a continuous sinusoidal loading wasmaintained on the load cell and the necessary actuator displacementneeded to maintain the programmed load was monitored. The sample to bemeasured was first placed between the test fixture discs and theactuator was positioned so that the preload force on the sample was 16.8g/cm² (0.24 psi) (corresponding to a load cell voltage output of 0.10volt). The 442 Controller was adjusted so that this positioncorresponded to an actuator LVDT output of zero volts. During theexperiment, the actuator position was adjusted by the 442 Controller sothat the force on the load cell varied sinusoidally between 1.36 and85.7 kg (3.0 and 188.5 pounds-force) corresponding to a sample loadingof 0.0168 and 1.055 kg/cm² (0.24 and 15.0 psi), respectively. Thevoltages corresponding to the position of the actuator and the force onthe load cell were monitored by the Nicolet 4094 Digital Oscilloscope.The stress-strain hysteresis loop was monitored until no changes due tosample relaxation were observed. Four consecutive hysteresis loops werethen stored in he oscilloscope pending analysis.

To obtain the resilience (% recovery) values, the MTS system was used inthe stroke control mode where a continuous sinusoidal displacement offixed amplitude was applied to the actuator and the resulting force onthe load cell was monitored. The sample to be measured was first placedbetween the test fixture discs and the actuator disc was positioned sothat the preload force on the sample was 16.8 g/cm² (0.24 psi)(corresponding to a load cell voltage output of 0.10 volt). The 442Controller was adjusted so that this position corresponded to anactuator LVDT output of zero volts. The distance between the disc faceswas measured and the 442 Controller was adjusted so that the maximumdisplacement of the actuator during the test would be exactly one-halfof the disc face distance. During the experiment, the actuator cycledsinusoidally between its zero position and a point at which the discface separation was 50% of the initial separation. The voltagescorresponding to the position of the actuator and the force on the loadcell were monitored by the Nicolet 4094 Digital Oscilloscope. Thestress-strain hysteresis loop was monitored until no changes due tosample relaxation were observed. Four consecutive hysteresis loops werethen stored in the oscilloscope pending analysis.

A variety of orthotic pads were prepared and their inverse moduli andresilience calculated according to the above procedures, the results ofwhich are listed below in TABLE I.

Resins were prepared as described in Example 2, using Isonate® 143L asthe isocyanate, and a final concentration in the resin system of 0.07%benzoyl chloride (as stabilizer), 4.0% MEMPE (as catalyst) and 0.2%butylated hydroxytoluene (as stabilizer). None of the samples containedplasticizer. As the polyol, Examples 3-8 were prepared in pairs usingtriols of varying OH equivalent weights (1650, 2000 and 1350,respectively) and Examples 9-14 were prepared in pairs using diols ofvarying OH equivalent weights (1500, 500 and 1000, respectively). Theodd-numbered Examples of each pair were prepared at an NCO:OH ratio of2.5:1, and the even numbered at 3:1.

The orthotic pads were each prepared using 1.9 cm (3/4 inch) thick foam("E-150") impregnated at an 85% resin system coating weight. The OHequivalent weight of the polyols used was varied as shown in TABLE I.Also listed in TABLE I are the subjective determination ("comments" ) ofthe suitability of each pad for use as an orthotic pad.

                                      TABLE                                       __________________________________________________________________________              Inverse                                                                       Modulus     Resilience                                              polyol(OH (% deformation)                                                                           (% recovery)                                            Ex. eq. wt)                                                                             Uncomp.                                                                             50% Comp.                                                                           Uncomp.                                                                             50% Comp.                                                                           Comments                                    __________________________________________________________________________    3   1650                                                                             triols                                                                           80    53    45    87    Excellent                                   4   1650                                                                             triols                                                                           76    42    51    91    "                                           5   2000                                                                             triols                                                                           80    57    40    82    "                                           6   2000                                                                             triols                                                                           78    47    46    90    "                                           7   1350                                                                             triols                                                                           77    42    51    92    "                                           8   1350                                                                             triols                                                                           78    44    49    91    "                                           9   1500                                                                             diols                                                                            80    47    30    81    Useful                                      10  1500                                                                             diols                                                                            80    50    35    78    "                                           11  500                                                                              diols                                                                            77    38    32    71    Stiff                                       12  500                                                                              diols                                                                            63    23    40    73    "                                           13  1000                                                                             diols                                                                            78    45    39    86    Useful                                      14  1000                                                                             diols                                                                            79    47    38    81    "                                           __________________________________________________________________________

As seen in TABLE I, preferable orthotic pads prepared as described inExamples 3-14 exhibit inverse moduli (in the uncompressed and 50%compressed states) of between about 40% and about 100% deformation, andpreferably between about 45% and about 90% deformation, in response to aload of 1.05 kg/cm² applied over a period of 0.5 seconds.Correspondingly, preferable orthotic pads prepared as described in theseExamples exhibit resilience (in the uncompressed and 50% compressedstates) of between about 30% and about 100% recovery, and preferablybetween about 40% and about 100% recovery, within 0.5 seconds, afterbeing deformed to one-half their cured thickness. Generally, suitableorthotic pads of the present invention will recover essentially all oftheir original shape within a reasonable period of time for use, e.g.,within seconds of their being deformed.

EXAMPLE 15

A resin impregnated open-celled foam was prepared in the followingmanner. The following resin system was impregnated into an open-celledfoam ("P-100 Foam", 1/8 inch×3 inch×8 feet (3.2 mm×76.2 mm×2.4 m),obtained from Technifoam Inc.) to a coating weight of 86%:

    ______________________________________                                        Isonate ™ 143L isocyanate                                                                         21%                                                    Butyl benzylphthalate  10%                                                    MEMPE                  1.5%                                                   Benzoyl chloride       0.06%                                                  LHT-42 ™ polyol     61.64%                                                 Pluronic F-38          4%                                                     (A polyethylene oxide-                                                        terminated polypropylene                                                      oxide, BASF Corp.)                                                            DB-100 ™            0.2%                                                   (A silicone oil - used as                                                     an antifoaming agent,                                                         Dow Corning)                                                                  Ionol ™ (butylated hydroxytoluene)                                                                0.33%                                                  "Reactint Yellow"      0.25%                                                  (A yellow dye, Milliken                                                       Chemicals)                                                                    Cab-o-sil ™         1%                                                     (Hydrophobic fumed silica,                                                    Cabot)                                                                        TOTAL                  100%                                                   ______________________________________                                    

Coating was performed under dryroom conditions and the resin impregnatedfoam was rolled and placed in a moisture proof pouch for storage. ThePluronic™ F-38 component was used to provide a non-tacky, or "slippery"feel to the surface of the impregnated foam upon water activation, inorder to improve the user's abiltity to handle the foam in the course ofunrolling and applying the roll. The Cab-o-sil™ silica was included as athixotrope to increase the viscosity of the resin, thereby limitingresin migration within and/or from the foam.

Rolls of the resin impregnated foam were used as cast padding for equinelimbs. The foam cast padding was applied to 40 clinical cases forevaluation of pressure sore prevention and compatibility of the resinwith the skin of the equine limb for both short and long term use. Castswere applied for a variety of time periods, depending on the clinicalsituation. They were applied mostly for immobilization of orthopedicinjuries, however, they were also used for treatment of flexural andangular limb deformities in foals as well as in the treatment of chroniclaminitis. In this latter application, the resin impregnated foam wasused for the protection of the sole surface of the foot.

Other materials used were synthetic stockinette, 1/8 inch×3/8 inch (3.2mm×76.2 mm) cast felt, and conventional fiberglass casting tape(Vetcast™ Plus Casting Tape, 3M). The resin impregnated foam was appliedas a thin layer to be used under the cast material and directly oversynthetic stockinette covering the limb. No additional padding was usedwith the exception of felt used to form a collar at the top of the cast.The foam was applied in a spiral application with a one-half widthoverlap starting proximally and spiraling down the limb. The overlapcreated a double layer of foam resulting in 1/4 inch (6.4 mm) of foambeing present over the entire limb from the carpus or tarsus to thecoronary band. A third layer of foam over the fetlock or over anincision was used in some instances. The foam material was then overlaidwith the fiberglass cast material applied in a conventional manner. Thecured cast material was left on the limb as appropriate for the clinicalcondition being treated, then removed by conventional means.

The fiberglass casting tape bonded tightly to the resin impregnatedfoam, with the foam essentially becoming part of the inner surface ofthe cast. The foam also bonded well to itself, i.e., at points ofcontact where overlapped, creating a single unit, the layers of whichwere visually indistinguishable. The resin impregnated foam conformedwell to the anatomy of the limb. It compressed more at the bonyprominences, such as over the sesamoids and it expanded into depressionson the surface of the limb, such as between the flexor tendons and thesuspensory ligament. This conformation of the cast to the limb virtuallyeliminated problems with pressure sores in the area of the sesamoid andat the heels of the foot, two places which are commonly trouble spotsfor pressure sores during clinical casting application.

In addition, the foam-lined cast maintained closer contact with agreater surface area of the limb than would ordinarily be seen withconventional fiberglass casts. This contact improved the ability toclosely adapt external cast immobilization to the limb for use insituations such as a fracture of the metacarpus. The foam created acomfortable " grip" on the limb without uneven application of pressureto the bony prominences. Therefore, a more rigid adaptation of the castfor a more rigid immobilization of the limb was the result. Casts couldbe applied more closely to the limb, thereby reducing the need foradditional underlying padding, and increasing the cast's ability tolimit motion between the limb and the cast and between segments of thelimb.

Pressure sores were occasionally encountered at the proximal end of thecast in the area where the dorsal aspect of the cannon bone would presstightly against the cast if ideal standing conformation of the cast wasnot attained. These pressure sores, however were primarily the result ofmisalignment of the limb and cast to the ground surface. They resultedfrom pressure of the cast material onto the vulnerable skin at the edgeof the cast as the horse stood on the limb.

Surprisingly, in situations where incisions or wounds were present onthe limb prior to cast application, the foam appeared to absorb exudateand wick it away from such incisions or wounds, thereby allowing theexudate to percolate through to the exterior of the cast much betterthan would be expected from traditional cotton cast padding. Woundsappeared to be both cleaner and dryer after removal of the cast thanwould be the case with conventional casting techniques involving cottoncast padding.

EXAMPLE 16

A patient's leg ulcer, located in the lower calf area of a human leg iscleaned, debrided, and medicated as the attending physician deemsnecessary.

The ulcerated area is covered by interface material(s) selected from oneor more of the following:

a clean stockinette

a wound dressing, such as sterile gauze

non-adherent wound contact material (e.g., Tegapore™ material, 3M)

A roll of resin impregnated foam padding prepared as described inEXAMPLE 15 is removed from its moisture proof pouch and activated bydipping in water. Water is pumped through the foam roll by squeezing.The activated, impregnated foam is wrapped over the ulcerated area,overlapping each wrap by approximately half. The activated, impregnatedfoam is followed by wrapping with an ACE™ bandage that compresses thefoam to approximately one-half of its initial thickness. The activated,impregnated foam cures in about 4 minutes, bonding the overlappinglayers of foam and the stockinette into a single unit.

The cured dressing closely replicates the shape and contours of the limband exhibits variable modulus and resilience. The porous nature of thecured dressing, together with the precise fit, serve to wick excessexudate away from the ulcer while maintaining a moist healingenvironment. The cured resin impregnated foam, in combination withcompression wraps and interface material(s), provides improvedcompression for the management of venous ulcerations, providing theopportunity for improved healing. Additionally, the cured foam can beremoved from the limb and reapplied with fresh interface materials.

We claim:
 1. A foam pad comprising an open-celled foam impregnated witha resin system, said resin system comprisinga. a water curableprepolymer resin comprising an isocyanate component and a polyolcomponent, said polyol component having an average hydroxyl equivalentweight greater than about 400 grams of polyol per hydroxyl group, and b.a catalyst capable of setting and curing said prepolymer resin uponexposure to water,wherein said pad is a wound dressing in fluid contactwith a wound.
 2. The foam pad of claim 1 wherein the foam pad closelyreplicates the shape and contours of a patient's body surrounding thewound and wicks away exudate from the wound.
 3. The foam pad of claim 2wherein the wound is on the patient's limb.
 4. The foam pad of claim 1wherein the foam pad closely replicates the shape and contours of the apatient's body surrounding the wound and is compressed against the bodyand wound without forming pressure sores.